Service Management Architectures Issues and Review

Network Working Group                                            M. Eder
Request for Comments: 3052                                         Nokia
Category: Informational                                           S. Nag
                                                            January 2001


          Service Management Architectures Issues and Review

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   Many of the support functions necessary to exploit the mechanisms by
   which differing levels of service can be provided are limited in
   scope and a complete framework is non-existent.  Various efforts at
   such a framework have received a great deal of attention and
   represent a historical shift in scope for many of the organizations
   looking to address this problem.  The purpose of this document is to
   explore the problems of defining a Service management framework and
   to examine some of the issues that still need to be resolved.

1. Introduction

   Efforts to provide mechanisms to distinguish the priority given to
   one set of packets, or flows, relative to another are well underway
   and in many modern IP networks, best effort service will be just one
   of the many services being offered by the network as opposed to it
   being the only service provided.  Unfortunately, many of the support
   functions necessary to exploit the mechanisms by which network level
   service can be provided are limited in scope and a complete framework
   is non-existent.  Compounding the problem is the varied understanding
   of exactly what the scope of "service" is in an IP network.  IP, in
   contrast to connection oriented network technologies, will not be
   able to limit the definition of service management simply to end to
   end connectivity, but will combine service management with regards to
   transport with the service requirements of the actual applications
   and how they are using the network.  The phenomenal growth in data
   networks as well as the growth in application bandwidth usage has had
   the consequence that the existing methods of management are not
   sufficient to handle the growing demands of scale and complexity.

   The network and service management issue is going to be a major
   problem facing the networks of the future.  This realization is a
   significant motivating factor in various efforts within the IP
   community which has been traditionally reluctant to take on issues of
   this type [1].  The purpose of this document is to explore the
   problems of developing a framework for managing the network and
   services and to examine some of the issues that recent efforts have
   uncovered.

2. The Problem of Management Standards

   Network and service level issues traditionally are handled in IP
   networks by engineering the network to provide the best service
   possible for a single class of service.  Increasingly there is a
   desire that IP networks be used to carry data with specific QoS
   constraints.  IP networks will require a tremendous amount of
   management information to provision, maintain, validate, and bill for
   these new services.  The control and distribution of management
   information in complex communications networks is one of the most
   sophisticated tasks a network management framework must resolve. This
   is compounded by the likelihood that devices in IP networks will be
   varied and have differing management capabilities, ranging from
   complex computing and switching platforms to personal hand held
   devices and everything in between.  Scaling and performance
   requirements will make the task of defining a single management
   framework for these networks extremely complex.

   In the past standardization efforts have suggested a simplified model
   for management on the hypothesis that it can be extrapolated to solve
   complex systems.  This premise has often proved to be without merit
   because of the difficulty of developing such a model that meets both
   the operators heterogeneous, multi-vendor need and network equipment
   vendors specific needs.  At the center of efforts to devise a
   standard management model are attempts to develop an architecture or
   framework to control the management information. The same conflicting
   operator vs. vendor forces are present in the effort to establish a
   common framework architecture as are in the efforts to develop a
   common information model.

   Network operators requirements call for a framework that will permit
   centralized management of the network and require the minimal
   resources to operate and maintain while still providing tremendous
   flexibility in choice of equipment and creativity of defining
   services [2].  Operators may be less able to support change in their
   Operational Support Systems (OSS) then they are in the network
   infrastructure because the OSS is tightly integrated into the
   organizations business practices.  The need for flexibility, and the
   other desires identified above, operators expect to have meet by
   having equipment vendors support open and common interfaces.

   Device manufactures have a need for management that will best
   represent the features and capabilities of the equipment they are
   developing and any management solution that hinders the ability of
   the equipment vendors to efficiently bring innovation to the market
   is contrary to their objectives.

   The common framework for solving the management needs of operators
   and equipment vendors has been based on a centralized approach with a
   the manager agent architecture.  While providing a very
   straightforward approach to the problem of information management,
   this approach, and its variations, has not proved to scale well or
   allowed the flexibility required in today's modern data networks.
   Scaling and flexibility are especially a problem where there are many
   sophisticated network devices present.  Methods of control must be
   found that work and scale at the same speeds as that of the control
   plane of the network itself if a major concern of the management
   system is with the dynamic control of traffic in a network.
   Increasingly it is a requirement that customers at the edge of the
   network be able to have access to management functionality.  A
   centralized management approach may not provide the most convenient
   architecture to allow this capability.

   Frameworks based on a decentralized approach to the management
   architecture have gained momentum in recent years, but must address
   the possibility of having redundant management information throughout
   the network.  A decentralized framework may have advantages with
   regards to scaling and speed of operation, but information and state
   management becomes complex in this approach, resulting in additional
   complication in developing such systems.

   The complexity of managing a network increases dramatically as the
   number of services and the number and complexity of devices in the
   network increases.  The success of IP networks can be partially
   traced to the successful separation of transport control mechanisms
   from the complexity of service management, including billing.  As the
   trend in IP is to allow for classes of traffic that will have both
   transport and service dependencies it has become apparent that many
   of the management problems are becoming more complex in nature and
   are starting to resemble those of the traditional telecom provisioned
   service environment.  In the telecom environment no such separation
   exists between transport control mechanisms and service.  The Telecom
   community has struggled for years to come up with a standard solution
   for the problem in national and international standardization bodies
   and achieved a debatable amount of industry acceptance.

   Unfortunately, the hard learned lessons of how to manage the
   interdependencies between service and transport will be of
   questionable use to the IP community because of the much more limited
   concept of service in the telecommunications environment.

   Rules based management has received much attention as a method to
   reduce much of the overhead and operator intervention that was
   necessary in traditional management systems.  The potential exists
   that a rules-based system could reduce the rate at which management
   information is increasing, but given the tremendous growth in this
   information, the problems with the control of that information will
   continue to exist.  Rules add additional issues to the complexity of
   managing a network and as such will contribute to the information
   control problem.

2.1. IP QoS Management

   Much of the current management efforts are focused on solving control
   issues for IP QoS [3].  A number of open questions exist with the IP
   QoS architecture which will make it difficult to define a management
   architecture until they are resolved.  These are well documented in
   "Next steps for the IP QoS architecture" [4], but from the management
   perspective warrant emphasizing.

   Current IP QoS architectures have not defined if the service will be
   per-application or only a transport-layer option.  This will have
   significant impact both from a control perspective and from a billing
   and service assurance one.

   The assumption is that the routing best effort path will be used for
   both best effort traffic and for traffic of a different service
   level.  In addition to those issues raised in [4], best effort path
   routing may not be able to identify the parameters necessary to
   identify routes capable of sustaining distinguished service traffic.

   In any architecture where a premium service will be offered it is a
   strong requirement that the service be measurable and sustainable.
   Provisioning that service will require a coherent view of the network
   and not just the device management view that is currently implemented
   in most networks.

2.2. Promise of rules-based Management

   Management standardization efforts in the IP community have so far
   been concerned primarily with what is commonly referred to as
   "element management" or "device management" [5].  Generally there is
   agreement as to the scope of element management.  Once outside that
   domain efforts to divide that task along clear boundaries have proved
   elusive with many of the terms being used having their roots in the
   telecommunications industry and as such being of potentially limited
   use for IP management [1].  Confusion resulting from the ambiguity
   associated with what functions compose management beyond those
   intended for the element, is compounded by the broad scope for which
   network and service management standards apply.  Terms such a
   business goals, service management, and application management are
   not sufficiently defined to insure there will not be disagreement as
   to the actual scope of the management functions needed and to what
   extent interrelationships will exists between them.

   It is within this hazy domain that much of the recent efforts in
   rules-based management have been proposed as a potential solution.
   Efforts to devise a framework for policy management is an example of
   one of the most popular recent activities.  Proposed requirements for
   policy management look very much like pre-existing network management
   requirements [2], but specific models needed to define policy itself
   and related to the definition of policy to control DiffServ and RSVP
   based QoS are under development.

2.3. Service Management Requirements

   Efforts to define the requirements for a service management system
   are hindered by the different needs of network operators.  In an
   industry where much has been written about the trend towards
   convergence there still exist fundamental differences in the business
   needs of operators.

2.3.1. Enterprise

   The management requirements from both the operations and the network
   perspective have some interesting characteristics in the enterprise
   environment when compared to the public network.  In the enterprise
   end to end traffic management is implemented without the burden of
   complex tariff issues.  Service Level Agreements, while increasing in
   the enterprise, do not have the same operations impact as in the
   public network.  The high costs associated with implementing non-
   reputable auditing systems are usually not present.  This results in
   a substantial reduction in the number of expressions necessary to
   represent a particular networks business model.

   In the world of best effort service, rules-based management presents
   the possibility to give the IT department a tool the make the network
   appear to not be overloaded by prioritizing traffic.  This is done by
   prioritizing delay sensitive traffic (Web browsing) from traffic that
   is not delay sensitive (Email) or by prioritizing the traffic from a
   particular location or source.  This will, depending on the composite
   of an enterprises traffic, increase the useful life of the network
   without adding additional capacity.  This does not come without
   tradeoffs.  Both the purchase and management costs associated with
   the system must be calculated as well as the cost of the added
   complexity of adding additional control information to the network.

2.3.2. Service Provider

   It has for a long time been a goal of service providers to have a
   centralized management system.  While the motivation for this is very
   straightforward there exist some fundamental obstacles in achieving
   this goal.  Service providers often do not want to be tied to a
   single vendor and certainly do not want to be limited to only one
   model of any single vendors equipment.  At the same time bottom line
   costs are of paramount importance which often result in networks not
   being as heterogeneous as operators would like. Centralized
   management implies a scalable system able to manage potentially many
   heterogeneous pieces of equipment.  The amount of data necessary to
   achieve this is contrary to the scalability requirement.  In response
   to this problem it has been attempted many times to identify the
   common model that represents the subset common to all devices.
   Unfortunately all too often this set is either too complex,
   increasing the cost of devices, or too limited to preclude large
   amounts of device specific data thus defeating the purpose. For such
   a management model to be successful at the service level, the
   services being modeled must be standardized.  This is counter
   intuitive to the competitive model of which the service provider
   operates.  To be successful speed to market has become a key element
   that differentiates one service provider from another.  Constraints
   placed on equipment manufacturers and the management infrastructure
   by a centralized management system are also detrimental to this goal.
   While for a limited set of well defined services a central management
   approach is feasible, such a system can very quickly become a major
   contributor to the very problems it was intended to solve.

3. Network and Service Management

   Currently many of the efforts to define a framework for management
   are described in very implementation independent terms.  In actual
   fact the implementation of that framework directly affects for what
   situations the management system will be most beneficial.  While many
   past attempts to define a common management framework have failed it
   may be in the area of service management that such efforts finally
   gain industry acceptance.  It may be in the domain of service
   management that information models can be defined that are
   sufficiently specific to be useful and at that same time not have a
   negative impact on the equipment or service providers business needs.

   This section will discuss some of the issues that need to be resolved
   with regards to a service management framework to meet the
   requirements of the modern IP network.

   Some of the key concerns looking at a management system architecture
   include:

      -  The management interface and models supported
      -  The management system architecture
      -  Where and how functionality is realized

3.1. Architecture for information management

   Networks will consist of network elements that have existed prior to
   efforts to define a standard information model, rules-based or
   otherwise, and elements deployed after.  This problem has been
   addressed by some of the recent efforts in policy management.  Those
   elements that take into account policy are termed policy aware while
   those that do not are termed policy unaware.  The distinction being
   made that aware devices can interpret the policy information model or
   schema.  These issues apply equally to other standard management
   information.  In reality it is unlikely that any device will be fully
   policy aware for long, as the policy information model evolves, early
   devices will be only policy aware for those aspects of the model that
   had been defined at the time.  Key to success of any management
   framework is ability to handle revision and evolution.  A number
   methods exists provide this functionality.  One is designing the
   information models so that it can be extended but still be
   practically used in their original form.  A second is to provide an
   adaptation or proxy layer.  Each has advantages and disadvantages.

   Methods that attempt to extend the original model often overly
   constrain themselves.  Where the existing model cannot be extended
   new branches must be formed in the model that contain core management
   functionality.

   Adaptation methods can create performance and scalability problems
   and add complexity to the network by creating additional network
   elements.  A similar situation exists if the management framework is
   so flexible as to allow network elements to store locally information
   or choose to have information stored remotely.  From a device
   perspective, the criteria will be if the device can afford the logic
   based on other requirements it is designed to meet, and if the
   information can be retrieved in such a way as to support the
   performance and scalability requirements that are the subject of the
   information.  A dichotomy exists where there will be information that
   for reasons of performance and scalability will be transferred
   directly to the network elements in some situations, and in other
   situations, will exist in the management plan.  IP management efforts
   have left the level of detail needed to define the actual location of
   the management information to the implementation.  In a service
   management framework it may be necessary to achieve the desired
   results to supply a more complete framework along the lines of detail
   provided by the ITU-T telecommunications management network efforts
   where the interfaces and functionality across interfaces has been
   clearly defined.

   Information will need to exist in multiple locations simultaneously
   in any network architecture.  As the quantity and complexity of that
   information increases limitations quickly develop.  Changes in the
   information may need to be propagated in close to real time, further
   adding to the complication.

3.1.1. Rules-based Management

   A network management framework can be viewed as being divided into
   two essential functions.  The first deals with the aspects of
   managing the management information while the second deals with the
   aspects of transferring that management information into the network.
   The fundamental difference between rules based management and
   existing network management standards is that the management
   information is expressed as rules that reflect a desired level of
   service from the network as opposed to device specific management
   information.  Many of the information management requirements of
   traditional management systems still apply in a rules-based
   environment.  The network is composed of specific devices and it is
   at the point where rules are conveyed as device specific management
   information that this form of management will encounter some of its
   greatest challenges.  A necessary component of a solution to this
   problem will be a generic information model to which rules can be
   applied and a framework architecture for distributing rules
   throughout the network.  The task of finding the proper generic model
   that is not too great a burden to implement and yet provides a level
   of detail sufficient to manage a network has proved to be
   historically extremely difficult.  In many ways the degree to which
   rules based management will be able to solve management problems is
   dependent on the success of efforts to define a generic model and
   have it be widely implemented [1].

   One concept often discussed along with policy deals with the
   integration of legacy devices into the policy framework.  The
   presumption is that legacy devices would be able to participate in
   the policy decision by having policy information translated into the
   native management interface.  For this to succeed a device would have
   to support a functionality for which policy would be specified. This
   would limit the usefulness of this approach to only information
   logically abstracted to the native interface of the device.  Given
   that existing standard management interfaces do not support such
   functionality, all such devices would need to have a proprietary
   interface implemented.  The interface being based on the existing
   interface supported by the device would potentially not have the
   scaling capabilities needed for a policy management system.  Unlike a
   standard network management interface, were management information
   can be distributed between the adaptation layer and the network
   element, rules based management information may not be so easily
   distributed.

   The framework for integrating rules based management system with
   existing network devices is not readily apparent and further study is
   needed.  The problem exists further when one considers that there
   will be early policy aware devices that may not be aware as the
   policy models are extended.  The partially policy aware devices may
   represent additional architectural issues as it may not be possible
   to expect consistency in what aspects of policy a given devices
   implements if there does not exist formal sets of mandatory
   functionality with clear evolution paths.  It is paramount if the
   policy management framework is going to able to evolve to accommodate
   the ever-increasing number of services likely to be supported by IP
   networks of the future that an evolution path be built into the
   framework.

3.2. Policy Protocol

   The need for a policy protocol is important in the context of a
   policy aware element that is performing a certain 'service'.  It is
   important to note here that not all elements will be aware of all
   service policies related to every service at all times.  Therefore it
   makes sense for an element to be aware of a certain service policy if
   that element is required for a given service at any instant in time.

   With the dynamics of a network where elements and links go up and
   down, a notion of a 'policy protocol' may become necessary.  The idea
   of a 'policy protocol' that runs in a multi-service network requiring
   multi-service policies.  For example; consider two arbitrary end
   nodes having multiple routing paths between them. Let's then assume
   that a certain path carries a certain service based on some Intserv
   bandwidth reservation technique.  Let's also then deduce that the
   elements along that path have some element specific policy statements
   that have been configured on them to support that requirement.  If
   now at any given instance any link or any element were to be
   unavailable along that path, the 'policy protocol' should be
   initiated to automatically go and configure the same service-policies
   on the elements along another routed path connecting the very same
   end points, so that there is no disruption in service and so that no
   human/operator intervention is required.

   The association of policy with the policy target is an area where
   considerable study may need to be done.  Some issues are if this
   needs to be explicitly done or if the policy can be so written that a
   common description of the target is also included?  Allowing a policy
   target to retrieve those policies that are relevant to it.

4. Conclusions

   Understanding the set of problems facing IP network management in
   general will be key in defining a comprehensive framework
   architecture that meets the needs of operators.  Additional risks are
   created by applying new management techniques to the management of IP
   networks.  The consequence of implementing management operations
   based on architectures that may not be compatible with existing
   management systems will still need to be explored.

   Given that many network devices in IP networks are making routing
   decisions based on information received via routing protocols it
   seems sensible that they also make QoS decisions in a similar
   fashion.

   Historically the broader the scope of a network management
   standardization effort the less likely it has been to succeed.
   Management standardization efforts must be careful to have clearly
   defined goals and requirements less they to experience the same fate
   as previous such efforts.

   As IP continues to extend it's concept of service beyond that of best
   effort to include, among other things, differentiate treatment of
   packets, it will become increasingly necessary to have mechanisms
   capable of supporting these extensions.  Efforts to define a common
   management model and framework have proven to be historically
   elusive.  Information models, whether they be traditional or rules-
   based, must address these past problems.  The desire to keep a
   competitive advantage, and the reality that a common model, to be
   truly common, will not provide sufficient detail to fully manage a
   device, has often slowed the acceptance on the part of equipment
   vendors to this approach.

   As IP continues to extend it's concept of service beyond that of best
   effort to include, among other things, differentiate treatment of
   packets it will become increasingly necessary to have mechanisms
   capable of supporting these extensions.

5. Security Considerations

   The exchange of management information in a network is one of the
   most sensitive from a security perspective.  Management protocols
   must address security to insure the integrity of the data.  A
   management architecture must provide for security considerations from
   its inception to insure the authenticity of the information provider
   and that the security mechanisms not be so cumbersome as to make them
   not feasible to implement.

6. Reference

   [1] Michael Eder, Sid Nag, Raj Bansal, "IP Service Management
       Framework", Work in Progress, October 1999.

   [2] Hugh Mahon, Yoram Bernet, and Shai Herzog, "Requirements for a
       Policy Management System", Work in Progress.

   [3] Yavatkar, R., Pendarakis, D. and R. Guerin, "A Framework for
       Policy-based Admission Control", RFC 2753, January 2000.

   [4] Huston, G., "Next Steps for the IP QoS Architecture", RFC 2990,
       November 2000.

   [5] McCloghrie, K. and M. Rose, "Management Information Base for
       Network Management of TCP/IP-based internets" RFC 1156, May 1990.

7. Authors' Addresses

   Michael Eder
   Nokia
   5 Wayside Road
   Burlington, MA  01803

   EMail: michael.eder@nokia.com


   Sid Nag
   PO Box 104
   Holmdel, NJ 07733

   EMail: thinker@monmouth.com

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